Pre-pit detector of optical recording medium

1. A pre-pit detector for an optical recording medium including a write surface on which an information write track for forming information pits carrying information data and pre-pit track previously having a plurality of pre-pits carrying information associated with the information write track are repeatedly formed in pairs, comprising: optical detection means having light reception surfaces split as first and second light reception surfaces in a tangential direction of said track, for receiving a reflected light of an optical beam irradiated to said write surface on said first and second light reception surfaces so as to output first and second optical detection signals corresponding to light reception intensities of said first and second light reception surfaces, and for receiving the reflected beam from said pre-pit track pairing up with said information write track to which the optical beam is irradiated, on said first light reception surface; a first amplifier for amplifying said first optical detection signal with a first gain; a second amplifier for amplifying said second optical detection signal with a second gain smaller than said first gain; subtraction means for computing a difference between output signals of said first and second amplifiers; and digitization means for digitizing the output signal of said subtraction means so as to generate said pre-pit detection signal, wherein a ratio of said first gain to said second gain (said first gain/said second gain) is set so that a ratio of the minimum value to the maximum value (minimum value 100/maximum value) of the output signal of said subtraction means corresponding to said pre-pit becomes greater than that when the ratio of said first gain to said second gain is one.

2. A pre-pit detector for an optical recording medium including an information write track and a plurality of pre-pits carrying information associated with the information write track, comprising: an optical detector having light reception surfaces split as first and second light reception surfaces in a tangential direction of said track, for outputting first and second light reception signals; a subtraction circuit for computing a difference between the first and second reception signals to output a radial push-pull signal; and a digitizing circuit for digitizing the radial push-pull signal to generate a pre-pit detection signal, wherein said subtraction circuit adjusts amplitude levels of the first and second light reception signals between which the difference is computed, at respective gains which are different from each other, so as to expand a digitizable range of the radial push-pull signal.

3. A pre-pit detector according to claim 2 , wherein said subtraction circuit comprises: a first amplifier for amplifying said first optical detection signal with a first gain; a second amplifier for amplifying said second optical detection signal with a second gain which is different from said first gain; subtraction means for computing a difference between output signals of said first and second amplifiers.

4. A pre-pit detector according to claim 3 , wherein a ratio of said first gain to said second gain is 1.3.